The present invention relates to an apparatus for detecting abnormalities in an electronic expansion valve incorporated into a medium pipe for a refrigerating machine of an air conditioner or refrigerator or the like.
FIG. 1 is a longitudinal sectional view showing the general configuration of an electronic expansion valve. In this figure, the electronic expansion valve 1 is configured from a cylindrical body 2, a magnet rotor 5 which is supported by a support rod 3 and a feed screw 4 inside the cylindrical body 2, a needle valve 6 which is attached to the lower end of the magnet rotor 5 and which passes through the inner side of the feed screw 4, a mounting base 7 which supports the cylindrical body 2, and a exciter coil 8 which is arranged to the outer side of the cylindrical body 2. A coolant pipe 9 is attached to the mounting base 7. In addition, to the mounting base 7 is formed an orifice 7a and the needle valve 6 is arranged so as to face the orifice 7a.
FIG. 2 is a view describing the position relationship between the magnet rotor 5 and the exciter coil 8 which configure a stepping motor. The exciter coil 8 is configured by the four coils L.sub.1 -L.sub.4 and the pulse currents P.sub.1 -P.sub.4 are successively supplied to these coils. FIG. 3 is a waveform diagram showing the displacement of the phases of these pulse currents P.sub.1 -P.sub.4 at this time.
In this manner, the coils L.sub.1 -L.sub.4 are successively supplied by the pulse currents P.sub.1 -P.sub.4 so that the magnet rotor 5 is rotationally driven in a stepwise manner. This rotational drive raises and lowers the needle valve 6 with respect to the orifice 7a, and performs adjustment of the degree of opening. This is to say that the amount of cooling medium which flows inside the coolant pipe 9 is controlled.
By the way, when the angle of opening of the needle valve 6 is adjusted so as to perform control of the amount of cooling medium, the needle valve 6 must be first lowered to the closed position, and several excitation pulses then given in the direction of opening of the exciter coil 8 so that the degree of opening of the needle valve 6 can be determined.
However, the degree of opening of the needle valve 6 determined in this manner is based on the assumption that the needle valve 6 is being driven to a position which corresponds to the number of excitation pulses and is not determined on the actual position which is detected for the needle valve 6. This creates a problem for detecting the actual position of the needle valve 6 when the electronic expansion valve 1 is incorporated into the coolant pipe 9 which is sealed.
Accordingly, when it is assumed that there is some sort of abnormality in the electronic expansion valve 1 since cooling medium flow control is not being performed well, it is necessary to cut the coolant pipe 9 and to separate the electronic expansion valve 1 and to confirm the actual action of the needle valve 6 with respect to the number of pulses.
However, when the electronic expansion valve 1 is re-incorporated, there is also the troublesome work of welding the coolant pipe 9 and injecting the cooling medium gas and so finding an abnormality in the electronic expansion valve 1 means much unnecessary work and expense.